init: make the command-line rewrite optional

init: make the command-line rewrite optional

When launched as PID 1 and after parsing its arguments, init wipes all
all of them except argv[0] and rewrites argv[0] to contain only "init",
so that its command-line appears solely as "init" in tools such as ps.

This patch adds the FEATURE_INIT_MODIFY_CMDLINE which, if set to n, will
make init preserve all its arguments including argv[0], be they parsed or
ignored.
The original command-line used to launch init can then be retrieved in
/proc/1/cmdline on Linux, for example.

Signed-off-by: Nicolas Carrier <nicolas.carrier@parrot.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>